This invention relates to an inspecting apparatus for inspecting the appearance of a pattern of a reticle for producing an integrated circuit.
In order to inspect the appearance of a reticle for producing an LSI (Large-Scale Integrated circuit), two methods are known. One of the two methods is xe2x80x9cdie-to-die inspectionxe2x80x9d of comparing identical patterns or dies on different locations on a single common reticle. The die-to-die inspection method is disclosed in Japanese Unexamined Patent Publication (JP-A) No. 10-282008 (282008/1998). The other of the two methods is xe2x80x9cdie-to-database inspectionxe2x80x9d of comparing a reticle pattern with CAD (Computer Aided Design) data used in drawing the reticle pattern.
Herein, the term xe2x80x9cdiexe2x80x9d is equivalent in meaning to a block of pattern area or its detected image for use as a unit to be subjected to pattern comparison. On the other hand, the term xe2x80x9cdatabasexe2x80x9d means a reference image synthesized from CAD data in contrast with an actual pattern image detected by an optical system.
A conventional reticle inspecting apparatus comprises an XY stage on which a reticle is mounted, an image-pickup optical system for picking up an image of a pattern of the reticle mounted on the XY stage as a picked-up image, an image input section for acquiring the picked-up image from the image-pickup optical system, a data converter for converting CAD data used in drawing the pattern of the reticle into a reference image, an image comparator for comparing the picked-up image and the reference image to detect a pattern defect, and a controller for controlling a whole of the apparatus.
In the conventional reticle inspecting apparatus described above, the stage with the reticle mounted thereon is moved and an image of a single frame of the pattern on the reticle is acquired by the image-pickup optical system and the image input section. The image thus acquired is transferred to the image comparator. On the other hand, the reference image is preliminarily obtained by conversion from the CAD data at the data converter and is sent to the image comparator in synchronism with the image. The image comparator compares the image and the reference image to detect any defect.
The single frame referred to herein is a unit of image which can be simultaneously processed by the image comparator.
Generally, as compared with an image acquiring time required in acquiring the image by the image-pickup optical system and the image input section, a transfer time required in transfer from the image input section to the image comparator, a data conversion time required in conversion of the CAD data, and an image processing time required in detection of any defect are considerably long. Therefore, in the conventional reticle inspecting apparatus of the above-mentioned structure, an image of a next frame acquired by the image input section can not be transferred unless a series of the above-mentioned defect detecting operations have been completed for a preceding frame. This results in occurrence of a latency.
In view of the above, time adjustment is carried out, for example, by decreasing a moving speed of the stage to delay the image acquiring time. Therefore, a whole inspecting time is unfavorably prolonged.
It is therefore an object of this invention to provide a reticle inspecting apparatus capable of shortening an inspecting time required in inspecting the appearance of a pattern of a reticle for producing an integrated circuit.
According to a first aspect of this invention, a reticle inspecting apparatus for detecting a pattern defect of a reticle for producing an integrated circuit comprises an XY stage on which the reticle is mounted; an image-pickup optical system for picking up an image of a pattern of the reticle mounted on the XY stage to obtain a picked-up image pattern having first through N-th (N being an integer not smaller than two) frames; first through M-th (M being an integer not smaller than two and not greater than N) image comparators; a distributor for distributing the first through the N-th frames of the picked-up image pattern to the first through the M-th image comparators one after another; and an inspection controller for converting CAD (Computer Aided Design) data used in drawing the pattern of the reticle into first through N-th intermediate data corresponding to the first through the N-th frames of the picked-up image pattern and for preliminarily transferring the first through the N-th intermediate data to the first through the M-th image comparators one after another. The first through the M-th image comparators compare the first through the N-th frames of the picked-up image pattern with first through N-th reference images produced from the first through the N-th intermediate data, respectively, to detect any defect in the first through the N-th frames of the picked-up image pattern.
According to a second aspect of this invention, the image-pickup optical system comprises a laser-scanning optical system and a transmitting light detector. The laser-scanning optical system produces a laser beam to scan in a Y direction a surface of the reticle mounted on the XY stage and moves the XY stage in an X direction perpendicular to the Y direction. The transmitting light detector detects a transmitting light obtained by transmission of the laser beam through the reticle to acquire each of the first through the N-th frames of the picked-up image pattern as a two-dimensional image pattern.
According to a third aspect of this invention, the first through the M-th image comparators transfer to the inspection controller detection results obtained by detecting any defect in the first through the N-th frames of the picked-up image pattern, respectively.
According to a fourth aspect of this invention, the distributor comprises first through M-th frame buffer memories for temporarily memorizing the first through the N-th frames of the picked-up image pattern, respectively. The distributor distributes the first through the N-th frames memorized in the first through the M-th frame buffer memories, respectively, to the first through the M-th image comparators one after another.
According to a fifth aspect of this invention, a reticle inspecting apparatus for comparing reference and comparison die patterns of a reticle for producing an integrated circuit to detect any defect in the patterns comprises an XY stage on which the reticle is mounted, an image-pickup optical system for picking up an image of the reference die pattern of the reticle mounted on the XY stage to obtain a picked-up reference die pattern having first through N-th (N being an integer not smaller than two) frames and thereafter picking up an image of the comparison die pattern of the reticle mounted on the XY stage to obtain a picked-up comparison die pattern having first through N-th frames, first through M-th (M being an integer not smaller than two and not greater than N) image comparators, and a distributor for distributing the first through the N-th frames of the picked-up reference die pattern to the first through the M-th image comparators one after another and thereafter distributing the first through the N-th frames of the picked-up comparison die pattern to the first through the M-th image comparators one after another. The first through the M-th image comparators comprise first through M-th die memories for memorizing the first through the N-th frames of the picked-up reference die pattern as first through N-th memorized frames. The first through the M-th image comparators compare with the first through the N-th memorized frames the first through the N-th frames of the picked-up comparison die pattern which are transferred following the first through the N-th frames of the picked-up reference die pattern to detect any defect between each of the first through the N-th frames of the picked-up reference die pattern and each corresponding one of the first through the N-th frames of the picked-up comparison die pattern.
According to a sixth aspect of this invention, the image-pickup optical system comprises a laser-scanning optical system and a transmitting light detector. The laser-scanning optical system produces a laser beam to scan in a Y direction a surface of the reticle mounted on the XY stage and moves the XY stage in an X direction perpendicular to the Y direction. The transmitting light detector detects a transmitting light obtained by transmission of the laser beam through the reticle to acquire each of the first through the N-th frames of the picked-up reference die pattern and the first through the N-th frames of the picked-up comparison die pattern as a two-dimensional image pattern.
According to a seventh aspect of this invention, the distributor comprises first through M-th frame buffer memories for temporarily memorizing the first through the N-th frames of the picked-up reference die pattern. The distributor distributes to the first through the M-th image comparators one after another the first through the N-th frames of the picked-up reference die pattern which are memorized in the first through the M-th frame buffer memories, respectively. Thereafter, the first through the M-th frame buffer memories temporarily memorize the first through the N-th frames of the picked-up comparison die pattern. The distributor distributes to the first through the M-th image comparators one after another the first through the N-th frames of the picked-up comparison die pattern which are memorized in the first through the M-th frame buffer memories, respectively.